linq如何建立一個where謂詞

Question

我想查詢形狀的IEnumerable。 我有不同種類的形狀，根據形狀的類型，它們以不同的方式與給定的坐標相關。

對於任何給定的坐標，我想找到它的相關形狀。 我想用Linq做到這一點。 但是由於缺乏了解而陷入困境。 搜索和閱讀已經花費了幾個小時，但是我可以找到正確的單詞來舉例說明我正在嘗試做的事情。 下面是一些代碼，希望能顯示我想做的概念，但顯然行不通。 必須有一種鏈接這些表達式的方法-我已經看過謂詞生成器並且可以使用它，但是我想首先學習更多基礎知識。 我該如何工作？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace LinqLearning
{
    public class Coordinate
    {
        public double X { get; set; }
        public double Y { get; set; }
    }
    public abstract class Bounded
    {
        public Coordinate TopRight { get; set; }
        public Coordinate BottomLeft { get; set; }
    }

    public class Shape1 : Bounded
    { }
    public class Shape2 : Bounded
    { }
    public class LinqExperiments
    {
        public IEnumerable<Bounded> GetSquaresNearPoint(IEnumerable<Bounded> shapesEnumerable, Coordinate locator)
        {
            Expression<Func<Bounded, Coordinate, bool>> Shape1NearCoordinate =
                (shape, coord) => shape.TopRight.Y > coord.Y &&
                                  shape.BottomLeft.Y < coord.Y &&
                                  shape.TopRight.X == coord.X;
            Expression<Func<Bounded, Coordinate, bool>> Shape2NearCoordinate =
                (shape, coord) => shape.TopRight.Y == coord.Y &&
                                  shape.TopRight.X < coord.X + 3 &&
                                  shape.TopRight.X > coord.X - 3;


            Expression<Func<IQueryable<Bounded>, Coordinate, bool>> predicate = (shapes, coord) => Shape1NearCoordinate || Shape2NearCoordinate;

            return shapesEnumerable.AsQueryable().Where(predicate);
        }
    }
}

Answer 1

我真的不明白為什么要使用Expression和IQueryable 。 我認為這可以通過Func<Bounded, Coordinate, bool>來解決：

    public IEnumerable<Bounded> GetSquaresNearPoint(IEnumerable<Bounded> shapesEnumerable, Coordinate locator)
    {
        Func<Bounded, Coordinate, bool> Shape1NearCoordinate =
            (shape, coord) => shape.TopRight.Y > coord.Y &&
                              shape.BottomLeft.Y < coord.Y &&
                              shape.TopRight.X == coord.X;
        Func<Bounded, Coordinate, bool> Shape2NearCoordinate =
            (shape, coord) => shape.TopRight.Y == coord.Y &&
                              shape.TopRight.X < coord.X + 3 &&
                              shape.TopRight.X > coord.X - 3;
        Func<Bounded, Coordinate, bool> predicate = (shapes, coord) => Shape1NearCoordinate(shapes, coord) || Shape2NearCoordinate(shapes, coord);
        return shapesEnumerable.Where(x => predicate(x, locator));
    }

Answer 2

為什么不堅持簡單的簡單功能呢？ 當真正不需要Lambda或Linq Expressions時，無需使用它們。

static bool Shape1NearCoordinate(Bounded shape, Coordinate coord) {
    return shape.TopRight.Y > coord.Y &&
            shape.BottomLeft.Y < coord.Y &&
            shape.TopRight.X == coord.X;
}

static bool Shape2NearCoordinate(Bounded shape, Coordinate coord) {
    return shape.TopRight.Y == coord.Y &&
            shape.TopRight.X < coord.X + 3 &&
            shape.TopRight.X > coord.X - 3;
}

public IEnumerable<Bounded> GetSquaresNearPoint(IEnumerable<Bounded> shapesEnumerable, Coordinate locator) {
    return shapesEnumerable.Where(shape => Shape1NearCoordinate(shape, locator) || Shape2NearCoordinate(shape, locator));
}